The use of devices to increase the pressure applied to the outer surface of pipe through cleaning brushes has been known for sometime. The patent issued to A. B. Carpmail, U.S. Pat. No. 2,353,125 on July 11, 1944 discloses a pipe cleaning apparatus with a three brush assembly having spring means to maintain, decrease and increase the pressure of the cleaning brush 50, FIG. 3 against pipe surface 32. In this particular disclosure is shown a spring 18 mounted on a threaded shaft 19, the tension in the spring 18 being adjustable by moving nut 23 to a new position. This type of spring arrangement is not desirable because the tension in the spring 18 will vary as the size of the pipe is changed. To maintain a constant brush pressure on the surface of the pipe would require a constant adjustment by repositioning nut 23. This is not only an inaccurate measurement of pressure against the pipe surface but also requires considerable loss of time in adjusting the spring tension as the size of the pipe is changed. It is also difficult to maintain consistent equal pressures on the pipe surface at all the brush stations.
The U.S. Pat. No. 2,427,129 issued to D. A. Fields on Sept. 9, 1947 like the Carpmail U.S. Pat. No. 2,353,125 previously disclosed shows in FIG. 3 the use of spring 42 to maintain pressure by the cleaning devices against the outer surface of the pipe. This spring requires adjustment to maintain proper pressure against the pipe when the size of the pipe is changed similar to the disclosure in the Carpmail U.S. Pat. No. 2,353,125.